we asked an imam some years back about giving cats commercial cat food, he said its okay, as long as it isnt anything inherently haram (ie. swine).
Coming back to the original question, can i feed our garden birds products made from non-halal beef suet (they dont use prok suet - if theres such a thing - its clearly labelled as beef). the reason i dont take the same ruling as above, is because in cases of pets, its your duty, but in cases of wild animals its just charity to Allahs creatures. actually putting it like that.. but can you?